The present invention pertains generally to systems for applying a coating material to a cylindrical object and more particularly to a base coat applicator for applying a base coat material to beverage cans.
Base coat applicator systems are used in the beverage container fabrication industry to apply a base coat material of a pre-determined thickness to the outer portions of a beverage container to provide a decorative background upon which a label can be applied. Depending upon the particular label to be applied, various thicknesses of base coat are required to provide the proper background appearance. Some labels require numerous or multiple layers of base coat material to achieve the proper decorative appearance of the can after the label is applied, while other cans may only require one or two layers of base coat material.
A disadvantage of conventional base coat applicator machines is that a single drive unit is used to drive both applicator wheels and turrets such that the machine is designed to apply a pre-determined number of base coat layers. The machine must, consequently, be modified to change the number of base coat layers applied. This results in costly down time if production line changes are desired to modify the appearance of a can or to process cans for different uses in a single production line. In this manner, flexibility of conventional base coat applicator devices is limited.
Additionally, since conventional base coat applicators use a common drive system for both the applicator wheel and turret, the speed of operation of the applicator wheel is directly dependent upon the inventory production speed of the applicator, i.e., the speed at which the applicator processes cans. At high inventory production speeds, an applicator wheel of a conventional base coat applicator must rotate at high speeds, especially where multiple layers must be applied to the can. High rotational speeds of the applicator wheel result in misting and slinging of the base coat material from the applicator wheel surface.
Another disadvantage of prior art base coat applicators is that drying of base coat material on various machine parts occurs if the machine must be shut down for any reason. This greatly delays restart of the system since base coat material must be removed before the base coat applicator can be used again.
Additionally, in order to achieve equal surface speeds between the can surface and the surface of the applicator wheel, drive wheels are employed in conventional base applicators which are substantially concentric with the applicator wheel. These drive wheels engage the mandrel substantially simultaneously with the engagement of the can and applicator wheel surface. Smearing of base coat material on the surface of the can occurs unless the mandrel reaches full rotational speed nearly instantaneously. Smearing of base coat material increases with increased inventory production speeds.